ANALYSIS OF THE SINGLE-FIBER PULL-OUT TEST BY THE USE OF RAMAN-SPECTROSCOPY .1. PULL-OUT OF ARAMID FIBERS FROM AN EPOXY-RESIN

Raman spectroscopy has been used to analyse the distribution of fibre strain in the single-fibre pull-out test by mapping the variation of strain along an aramid fibre undergoing pull-out from an epoxy resin matrix. Both sized and de-sized aramid fibres have been used in room-temperature and high-temperature cured resins. At low strains the behaviour follows conventional shear-lag analysis but as the fibre strain is increased yielding can take place in the matrix at the fibre/matrix interface. It is found that failure eventually takes place by either fibre/matrix de-bonding or fibre fracture outside the resin matrix. The presence of radial stresses at the interface has been found to be important. They are induced by thermal shrinkage upon cooling the hot-cured resin to room temperature and can also be caused by Poisson contraction during the pull-out process. They result in the measured values of interfacial shear stress being significantly different from those found for fully-embedded fibres.